RV 8 rear battery earth point

[MHarris]

I’m at the point of running all the wiring in the fuselage. With a rear mounted battery are people running a separate earth wire to the firewall or connecting the earth close to the battery location ?

 

[rv8ch]

I’m at the point of running all the wiring in the fuselage. With a rear mounted battery are people running a separate earth wire to the firewall or connecting the earth close to the battery location ?

I have done it 3 different ways: 1) ran the ground all the way to the front; 2) local ground in the tail on one of the thicker angles back there; 3) put the battery on the firewall, and then have a good single ground point on the FW. The reason for the changes are too long to go into now, but the main driver for moving the battery to the front is the super light earthx lifepo4 batteries saved a lot of weight, and not having 10 feet of fat cable go to the tail also saved a lot of weight. The 15-30 lbs of battery mass that was in the back is now available for my passenger to take more clothing when we travel.

 

[pauldan181]

I just ran a short #2 wire to the battery tray and made sure the bottom of the tray where it screws to the fuse structure was bare metal. My 0-360 cranks just fine.

 

[Mikeyb]

I used a rear mounted battery with the ground connected to the aft lower longeron as per Vans. I did it to optimize the solo CG. The trouble is Vans designed the aft mount when batteries were 25 pounds. With the modern batteries using the aft location only changes the CG a few tenths of an inch. If I did it again I would use a forward mount like Mickey did. Just the #2 wire run to the firewall was 3.5 pounds and there is more resistance using the airframe ground that reduces the buss voltage on startup.
mike

 

[chrispratt]

I used a rear mounted battery with the ground connected to the aft lower longeron as per Vans. I did it to optimize the solo CG. The trouble is Vans designed the aft mount when batteries were 25 pounds. With the modern batteries using the aft location only changes the CG a few tenths of an inch. If I did it again I would use a forward mount like Mickey did. Just the #2 wire run to the firewall was 3.5 pounds and there is more resistance using the airframe ground that reduces the buss voltage on startup.
mike

+1. I use the traditional heavy style battery in the back to help offset the nose heavy CG tendency of RV-8s with a CS prop. I used the left side longeron as Van's instructs. No issues in 19 years of operation.

Chris

 

[Ironflight]

Liek everyone else - I use the lower longeron to ground the aft-mounted battery in the R-8, and am doing the same thing in the F1 we’re building. Come to think of it, I built the RV-3 the same way….I must’ve in a rut……

 

[N804RV]

Here's how I did it. Its similar to photos I've seen of others. A milliohm meter showed that total resistance from the battery ground point to the firewall ground to be well within limits.

 

[MHarris]

Thanks very much for all your advice

 

[chaskuss]

I attached an angle to the main longeron. My thinking was:

#1 Don't attach wire directly to any longeron directly, because any future corrosion will weaken the longeron and be difficult to repair.
#2 Drilling a hole in a longeron without some sort of a doubler will weaken it.
#3 The main longeron goes directly to the firewall as a single piece of aluminum, so will have the least resistance for the starter motor due to multiple riveted connections.

 

[Little Wing]

Lower longeron